In the processing of semiconductor wafers, plasmas are used for etching and sputtering. In batch processing systems, precision in starting and controlling the plasma has not been critical. Recently there has been a turn toward automated serial processing of wafers. Serial production has made timing of steps more critical, and automation has made independence of controls essential. Thus, it is becoming more important to provide systems which ignite a plasma quickly and control the power delivered precisely.
An impedance matching network is often used to efficiently couple the radio-frequency (RF) power into the plasma. The parameters of the matching network must be adjustable to permit tuning to compensate for shielding, wafer size, gas pressure and other changing parameters of the system. Matching networks in the prior art have reactance phase and impedance magnitude controls which are highly interdependent. This interdependence is undesirable for use in an automated system.